¿Qué texto te entrega al declarar el error, aparte de debug failed?
Debug build of project `C:\a\a.mcp' started.
Preprocessor symbol `__DEBUG' is defined.
Thu Jan 29 13:56:29 2009
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Make: The target "C:\a\rs232.o" is out of date.
Executing: "C:\Archivos de programa\Microchip\MPASM Suite\MPASMWIN.exe" /q /p16F84A "C:\16f84a\rs232.asm" /l"rs232.lst" /e"rs232.err" /o"rs232.o" /d__DEBUG=1
Error[129] C:\16F84A\RS232.ASM 1 : Expected (END)
Halting build on first failure as requested.
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Debug build of project `C:\a\a.mcp' failed.
Preprocessor symbol `__DEBUG' is defined.
Thu Jan 29 13:56:30 2009
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BUILD FAILED